1. Field of the Invention
The present invention relates to an apparatus for and method of driving an ink-jet recording head used in a printer, a facsimile, a copier and the like. More particularly, the present invention relates to a technique of controlling an amount of a discharged ink drop.
2. Description of the Related Art
Conventionally, an ink-jet type recorder employing an ink-jet recording head has been well known. The ink-jet recording head used in this ink-jet type recorder is equipped with a plurality of nozzles in a vertical scanning direction or an advancing direction of a paper, and is moved to a horizontal scanning direction or an orthogonal direction to the advancing direction of the paper by a carriage mechanism. The nozzles of the ink-jet recording head discharge ink drops respectively at predetermined timings in accordance with a dot pattern data produced by spreading out print data. Accordingly, the ink drops from the respective nozzles are deposited on a record paper to thereby carry out a printing operation. In the ink-jet type recorder described above, the print is carried out by whether or not discharging the ink drops, namely, by controlling an on/off of dot. Thus, the above-mentioned ink-jet type recorder can not represent a halftone, such as a gray.
Therefore, a method of composing one pixel by a plurality of dots is employed to represent the halftone. In this method, when one pixel is represented by a dot matrix of 4xc3x974, the shade can be represented by 16 tones (17 tones, if including a pure white). Increase of the number of dots per pixel enables the representation of further fine tones. However, a substantial resolution is reduced if the tone is made finer without changing a dot diameter. Also, if a diameter of a record dot formed on the record paper is large, this makes the graininess in a low concentration area prominent, which accordingly reduces the quality of print.
Those problems can be solved by reducing the weight of the ink drop and making the diameter of the record dot thinner. However, the thinner diameter of the record dot causes a print speed to be slower. In order to prevent from the decrease of this print speed, such a technique may be considered that a discharge interval of the ink drops is made shorter, or the number of nozzles is increased but neither is easy.
In order to solve above-mentioned problems, Japanese Laid Open Patent Application (JP-A-Heisei 9-11457) discloses xe2x80x9can apparatus for driving an ink-jet recording headxe2x80x9d, which can control an amount of ink drops is charged from one nozzle and accordingly changing a size of a record dot to thereby carry out a fine tone representation. In this driving apparatus, a drive signal is sent to a piezoelectric device mounted correspondingly to each of a plurality of nozzles. The piezoelectric device is expanded and contracted in accordance with the supplied drive signal. Thus, the expansion and contraction causes a pressure change in a pressure room (in which ink is accommodated) mounted correspondingly to each of the plurality of nozzles. As a result, ink drops with an amount in accordance with the pressure change are discharged from each nozzle.
The drive signal used in this driving apparatus is generated by simultaneously generating a plurality of waveform signals having shapes different from each other, and then selecting one waveform signal from the plurality of waveform signals, in accordance with a print data. Accordingly, the amount of inks discharged from the nozzle is controlled in accordance with the waveform signal, a diameter of a record dot deposited on a record paper can be changed.
Also, Japanese Laid Open Patent Application (JP-A-Heisei 10-81012) discloses xe2x80x9can apparatus for and a method of driving an ink-jet type printer headxe2x80x9d, which is operated under the principle similar to the above-mentioned apparatus for driving an ink-jet recording head. A drive signal used in this driving apparatus includes four drive pulses within a print period required to generate one record dot. Then, in every print period, one or more drive pulses selected from the four drive pulses in accordance with a print data are sequentially sent to a pressure generation device.
Accordingly, the pressure generation device causes the pressure change in accordance with the drive pulse. Thus, the amount of ink drops is discharged on the basis of this pressure change. Hence, when one drive pulse is sent to the pressure generation device, one ink drop is discharged within the print period. When a plurality of drive pulses are sequentially sent to the pressure generation device, a plurality of ink drops are discharged within the print period. Accordingly, the amount of inks deposited on a record paper can be controlled to thereby control the diameter of the record dot.
Moreover, Japanese Laid Open Patent Application (JP-A-Heisei, 10-81014) discloses xe2x80x9can apparatus for and a method of driving an ink-jet type printer headxe2x80x9d, which uses a drive signal composed of three drive pulses, and controls an amount of inks deposited on a record paper to thereby change a diameter of a record dot. So, this is not the above-mentioned drive signal composed of the four drive pulses as noted in Japanese Laid Open Patent Application (JP-A-Heisei, 10-81012).
If the apparatus for driving an ink-jet recording head is used, which is disclosed in the above-mentioned Japanese Laid Open Patent Application (JP-A-Heisei 9-11457), a print speed can be improved without increasing the number of nozzles. However, it is necessary to mount hardware (actually, a transfer gate) to select one waveform signal from the plurality of waveform signals in response to each of the plurality of piezoelectric devices. Thus, the amount of hardware is extremely vast. For example, in such a case that the amount of ink drops is varied in three stages, the transfer gate equal to three times the number of nozzles are required. This results in a problem that the driving apparatus can not be made compact and its cost becomes expensive.
Also, if the techniques disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-81012) and Japanese Laid Open Patent Application (JP-A-Heisei 10-81014) are used, the print speed can be improved without increasing the number of nozzles and it is not necessary to select one waveform signal from the plurality of waveform signals. Thus, the hardware to select the waveform signal is not required. However, at least one drive pulse among a plurality of drive pulses outputted for each print period is generated such that a part of the drive signal is substantially equal to a Helmholtz period. Hence, there is a limit in making the print period shorter to thereby make the print speed faster. Also, the drive pulses according to the amount of the ink drop to be discharged from the plurality of drive pulse in the print period are sequentially sent to the pressure generation device. Hence, the discharge timing of the ink drop is different depending on the drive pulse to be sent. This results in a problem that a positional deviation of the deposition of the ink drop is induced to thereby deteriorate the quality of print. For example, a temporal period between first and third pulses is half the print period. Hence, a dot of the first pulse and a dot of the third pulse are deviated by a half pitch from each other. If the dot pitch is defined as 720 dot/inch (=35 xcexcm), they are deviated by 18 xcexcm from each other.
The present invention is accomplished in view of the above mentioned problems. Therefore, an object of the present invention is to provide an apparatus for and a method of driving an ink-jet recording head, which are small and cheap and can control an amount of ink drops discharged from a nozzle so as to make a print speed faster and also improve a print quality.
An apparatus for driving an ink-jet recording head, according to a first aspect of the present invention, includes a drive waveform generation circuit, a waveform extraction circuit. The drive waveform generation circuit generates a drive waveform in which n basic waveforms are connected in series, each of the n basic waveforms having a single period, where n is an integer equal to or greater than 2. The waveform extraction circuit which extracts m (m is an integer, and 0xe2x89xa6mxe2x89xa6n) of the n basic waveforms as a print drive waveform based on an externally supplied print data, and applies the print drive waveform to the piezoelectric device. Thereby, an ink is discharged from a nozzle based on a distortion of the piezoelectric device.
A method of driving an ink-jet recording head, according to a second aspect of the present invention, includes a generating step, an extracting step and an applying step. The generating step generates a drive waveform in which n basic waveforms are connected in series, each of the n basic waveforms having a single period, where n is an integer equal to or greater than 2. The extracting step extracts m (m is an integer, and 0xe2x89xa6mxe2x89xa6n) of the n basic waveforms as a print drive waveform based on an externally supplied print data. The applying step applies the print drive waveform to a piezoelectric device to thereby discharge an ink from a nozzle based on a distortion of the piezoelectric device.